Installation for hydrogen production and methods for using same

ABSTRACT

An installation and process for producing hydrogen, which includes a purification unit for purifying a hydrogen-rich synthesis gas and for producing hydrogen and a waste gas, along with the additional equipment required in order to continue operation in the event of a purification unit shutdown.

BACKGROUND

The invention relates to an installation for producing at leasthydrogen, this installation comprising at least:

-   -   a purification unit for purifying a hydrogen-rich synthesis gas        and for producing hydrogen and a waste gas,    -   a first line (5; 105) for conveying the synthesis gas to the        purification unit,    -   a second line (9: 109) for conveying the waste gas from the        purification unit to burners, and    -   a buffer tank (14) placed in the second line.

The invention also relates to a method to be employed when operatingthis installation, following an unscheduled shutdown of the purificationunit.

Furthermore, the invention relates to a method for starting up certainsorts of installations of the aforementioned type and to a method fordecreasing the hydrogen yield produced by same.

In an installation of the aforementioned type, the purification unitproduces a waste gas which is recovered in order to be burned in theburners, to which the supply is interrupted during an unscheduledshutdown of this purification unit, which is disadvantageous.

In particular, this installation may be equipped with a methanereforming unit, this reforming unit being heated and provided for thepurpose with burners in which the waste gas is burned. In such aconfiguration, an accidental shutdown of the purification unit oftenresults in the shutdown of the reforming unit. This is a drawback, andis especially serious because the time required to restart thisreforming unit amounts to tens of hours, all very costly. Furthermore,even in cases where the reforming unit is successfully kept inoperation, it can only return to steady state conditions after severalhours.

In consequence, numerous efforts have been made to improve thereliability of the purification units employed. However, thesepurification units still tend to stop accidentally.

The object of the invention, which aims in particular to correct theaforementioned drawback, is therefore to improve the operation and/orprofitability of an installation of the aforementioned type.

SUMMARY

To achieve this, the subject of the invention is an installation of thistype, characterized in that it comprises a third line which is equippedwith a first flow control valve and connects the first line to thesecond line.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects for the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 is a schematic and simplified view of an installation accordingto the invention and designed to produce hydrogen from a gas containingmethane; and

FIG. 2 is a schematic and simplified view of an installation accordingto the invention and designed to produce hydrogen and carbon monoxidefrom a gas containing methane.

DESCRIPTION OF PREFERRED EMBODIMENTS

To achieve this, the subject of the invention is an installation of thistype, characterized in that it comprises a third line which is equippedwith a first flow control valve and connects the first line to thesecond line.

According to other advantageous features of this installation:

-   -   a second flow control valve is provided downstream of the buffer        tank, the third line being connected to the second line        downstream of this second valve;    -   it comprises at least a first and a second flowmeter that are        placed to measure the flow rates in the first and the second        valves respectively, and also a unit for controlling these flow        rates and for calculating and controlling the degree of opening        of each of the first and second valves;    -   the purification unit is of the selective adsorption type with        cyclic pressure variation;    -   it comprises a unit (1; 101) for reforming methane with steam,        which is provided with said burners for its heating and which is        intended for producing the hydrogen-rich synthesis gas, the        purification unit being located downstream of the reforming unit        and intended for producing hydrogen extracted from the synthesis        gas;    -   it comprises a reactor for converting carbon monoxide to carbon        dioxide, placed between the reforming unit and the purification        unit, the third line being connected to the first line        downstream of this conversion reactor;    -   it comprises a separation unit located between the reforming        unit and the purification unit and intended to extract the        carbon monoxide present in the synthesis gas, and also a fourth        line which is equipped with another flow control valve and        connects the first line to the second line, the third and fourth        lines being connected to the first line downstream and upstream        of the separation unit respectively:    -   the separation unit is a cryogenic separation cold box;    -   a carbon dioxide purification device and a desiccation device        are placed between the reforming unit and the separation unit,        the fourth line being connected to the first line upstream of        the carbon dioxide purification device and of the desiccation        device.

The subject of invention is also a method for operating an installationas described hereinabove, in which:

-   -   in the purification unit, the hydrogen present in the synthesis        gas is extracted and a waste gas is recovered,    -   this waste gas is stored in the buffer tank, and    -   said burners are supplied at least with the waste gas stored in        the buffer tank, this method being characterized in that,        following an unscheduled shutdown of the purification unit:    -   the burners continue, at least initially, to be supplied with        waste gas, employing the gas stored in the buffer tank,    -   the first flow control valve is opened progressively, in order        to supply the burners with an increasing quantity of replacement        gas consisting of at least a portion of the synthesis gas.

According to other advantageous features of this method, it comprisesthe steps in which:

-   -   the second flow control valve is progressively closed,    -   the flow rate of the waste gas supplied to the burners is        measured continuously,    -   the theoretical flow rate of replacement gas to be burned in        order to compensate for the decrease in flow rate of the waste        gas supplied to the burners is continuously calculated in real        time, and    -   the actual flow rate of the replacement gas supplied to the        burners is regulated about said calculated theoretical flow        rate, by adjusting the degree of opening of the first flow        control valve.

Furthermore, the subject of the invention is a method for starting up aninstallation as defined above, characterized in that it comprises:

-   -   a first step in which the methane reforming unit is        progressively started up by supplying the burners with at least        a portion of the synthesis gas produced by this reforming unit,        this portion of the synthesis gas being taken by means of the        third line, and    -   a second step in which the purification unit, which produces a        waste gas, is started up, and the burners are supplied with an        increasing share of waste gas progressively replacing the        portion of synthesis gas supplied to the burners.

Furthermore, the subject of invention is a method for reducing thehydrogen yield produced by an installation as defined above, in which:

-   -   in the reforming unit, the gas containing methane is reacted        with steam, to produce a hydrogen-rich synthesis gas,    -   in the purification unit, the hydrogen present in the possibly        pretreated synthesis gas is extracted, and a waste gas is        recovered,    -   the burners are supplied with this waste gas, and    -   the heating of the reforming unit is supplemented by burning an        auxiliary fuel, characterized in that, at least initially:    -   the flow rate of synthesis gas for treatment in the purification        unit is reduced, by removing a portion thereof by means of the        third line,    -   this portion is used to supply the burners,    -   and the flow rate of the supplementarily burned auxiliary fuel        is simultaneously reduced.

In these figures, the solid lines which symbolize flow lines aredirected to indicate the directions of flow of the fluids in each of thetwo installations shown. Similarly, the dotted lines which symbolizelines for conveying monitoring and control data are directed to indicatein which direction this data flows.

Furthermore, the installations shown are organized in a conventional andwell-known basic arrangement. In FIGS. 1 and 2, this basic arrangement,which is actually complex, is therefore simplified by omitting certaincomponents largely known per se, solely for the sake of clarity.

An installation according to the invention is shown in FIG. 1. It is aninstallation for producing hydrogen from a gas containing methane, suchas natural gas. It comprises a unit 1 for reforming methane with steam,designed to be supplied with pressurized natural gas NG via a line 2,and for producing a hydrogen-rich synthesis gas as output, a reactor 3for converting carbon monoxide to carbon dioxide, placed downstream ofthe reforming unit 1, and a purification unit placed downstream of theconversion reactor 3 and designed to extract the hydrogen present in thesynthesis gas and to produce a waste gas. A line 5 for conveying thesynthesis gas at high pressure connects the outlet of the reforming unit1 to the inlet of the conversion reactor 3 and the outlet of the latterto the purification unit 4.

For its heating, the reforming unit 1 comprises burners 6 equipped withan atmospheric air intake 7. These burners 7 are designed to be suppliedwith natural gas conveyed by means of a line 8 branched off the line 2,and also with waste gas, at low pressure, produced by the purificationunit 4. This waste gas is conveyed by a line 9 from the purificationunit 4 to the burners 6.

The air flow rate in the air intake 7 is intended to be regulated by avalve 10 and measured by a flowmeter 11. The air intake may be equippedwith a blower, in which case the air flow rate measured by the flowmeter11 may be regulated by controlling this blower.

The line 8 itself is provided with a valve 12 and with a flowmeter 13,respectively intended to regulate and to measure the flow rate of thenatural gas supplied to the burners 6.

Since the purification unit 4 is of the type based on selectiveadsorption by cyclic pressure variation, a buffer tank 14, designed todampen the variations in flow rate of the waste gas leaving thispurification unit 4, is placed in the line 9 through which this wastegas upstream of the burners 6 flows. A valve 15 for regulating the rateof the flow leaving the buffer tank 14 and a flowmeter 16 for measuringthis flow rate are also provided in the line 9.

A line 17 connects the lines 5 and 9 which convey the synthesis gas andthe waste gas respectively. More specifically, this line 17 is connectedto the line 5, between the conversion reactor 3 and the purificationunit 4, and to the line 9, downstream of the valve 15 and of theflowmeter 16. It is equipped with a valve 18 for regulating the flowrate of the synthesis gas that it conveys, and also a flowmeter 19 formeasuring this flow rate.

The purification unit 4 comprises an outlet for the hydrogen produced,to which a line 20 for removing same is connected.

A unit 21 for monitoring, calculating and controlling the flow rates ofair, natural gas, waste gas and synthesis gas that are supplied to theburners 6 is designed, on the one hand, to receive a flow ratemeasurement from each of the flowmeters 11, 13, 16 and 19 and, on theother hand, to calculate and control the degree of opening of each ofthe valves 10, 12, 15 and 18.

In steady-state operation, the valve 18 is closed, so that the burners 6only burn waste gas and auxiliary natural gas. The installation shown inFIG. 1 accordingly operates in a manner that is known per se.

In case of sudden and unscheduled shutdown of the purification unit 4,said unit is automatically isolated from the rest of the installation,and the buffer tank 14 is no longer supplied with waste gas. Themonitoring, calculation and control unit 21 immediately actuates theprogressive closure, at a preset rate, of the valve 15. Simultaneously,it calculates, in real time and continuously, the theoretical flow rateof synthesis gas that must be burned in order to compensate for thedecrease in flow rate of the waste gas supplied to the burners 6, and itopens and controls the valve 18 in order to regulate, about thetheoretical flow rate that it has calculated, the actual flow rate ofthe synthesis gas supplied to the burners 6. The calculation in questiontakes account of the calorific values of the waste gas and the synthesisgas.

As a variant, the degree of opening of the valve 18 is not calculated asa function of the measurement taken by the flowmeter 16, but it is thedirect consequence of the regulation of a temperature connected with theoperation of the burners 6, like the temperature of the combustion gasesor the temperature of the reforming reaction.

The substitution of the waste gas by a portion of the synthesis gascannot take place instantaneously because of the response time of theequipment, particularly the valves, that are then involved. Thus, thebuffer tank 14 makes the transient progressive substitution phasedescribed above possible. After this phase is completed, the reformingunit 1 has preserved a stable operating regime, although its burners 6are now only supplied with natural gas and synthesis gas, since valve 15is closed.

The purification unit 4 can then be promptly restarted. This saves time,amounting to tens of hours, normally required to restart the reformingunit 1.

We shall now attempt to describe an advantageous procedure for startingup the installation shown in FIG. 1. This procedure comprises a firstand a second step. In the first step, the reforming unit 1 is started upprogressively by supplying the burners 6 with at least a portion of thesynthesis gas produced. The flow rate of this portion, which flows inthe line 17, is determined by the degree of opening of the valve 18,which is controlled by the unit 21.

In the second start-up step, the purification unit 4 is started up bysupplying it with an increasing flow rate of synthesis gas. Thispurification unit 4 then produces hydrogen and waste gas which isprogressively substituted with the synthesis gas supplied to the burners6.

The combustion of synthesis gas in the burners 6 serves to economize thefuel that would otherwise have to be consumed during start-up of theinstallation.

A procedure will now be described that can advantageously be employedwhen it is desirable to rapidly reduce the quantity of hydrogenproduced.

The reforming unit 1 and the purification unit 4 both exhibit someinertia, so that the quantity of hydrogen produced cannot be reducedinstantaneously. The reforming unit 1 evolves more slowly than thepurification unit. Therefore, in the prior art, it is this thatdetermines the rate at which the quantity of hydrogen produced isreduced. If this rate is lower than the desired rate, the surplushydrogen is burned in a flare.

If, in the installation shown in FIG. 1, it is decided to slow thepurification unit 4 faster than can be done with the reforming unit 1,the portion of synthesis gas that is no longer supplied to thepurification unit 4 can be removed via the line 7, and burned in theburners 6. This accordingly reduces the flow rate of natural gassupplied to these burners 6, thereby achieving a saving.

As a variant, the location of each of the two connections of the line 17to the lines 5 and 9 respectively can be shifted. If the connection ofthis line 17 to the line 9 is placed upstream of the buffer tank 14, itis possible, during the transition procedures described hereinabove, tocontrol the valve 18 in order to regulate the pressure of the buffertank 14, the valve 15 then being controlled to a setpoint value by theflow rate regulation in the line 9. This is done by applying acorrection to the measurement taken by the flowmeter 16, in order totake account of the change in composition of the gas flowing throughthis line 9.

FIG. 2 shows an installation for producing hydrogen and carbon monoxidefrom natural gas. This installation is designed in an arrangementroughly similar to the installation shown in FIG. 1. Thus we shall onlydescribe hereinbelow what distinguishes it from this installation shownin FIG. 1, of which the components are identified by reference numeralswhich are increased by 100 in order to denote, in what follows, thesimilar components of the installation illustrated in FIG. 2.

The reactor 3 for converting carbon monoxide to hydrogen is replacedwith a carbon dioxide purification device 22, a desiccation device 23,placed downstream of the purification device 22, and a separation unitformed by a cryogenic separation cold box 24. This cold box 24 is placeddownstream of the desiccation device 23. It is designed to extract thecarbon monoxide present in the synthesis gas passing through it.

In addition to carbon monoxide, for the removal of which a line 25 isconnected to the cold box 24, the latter is designed to produce a wastegas. A line 26 for transporting this waste gas connects the cold box 24to the line 109, to which it is connected downstream of the valve 115and of the flowmeter 116. The line 26 is equipped with a control valve27 and with a flowmeter 28. The valve 27 is designed to be controlled bya monitoring, calculation and control unit 21, as a function of themeasurement taken by the flowmeter 28.

The line 17, which connects the lines 109 and 105, is connected to thelatter between the cold box 24 and the purification unit 104.

Another line, with reference numeral 29, also connects the line 105 tothe line 109, to which it is also connected downstream of the valve 115and of the flowmeter 116. Its connection to the line 105 neverthelessdistinguishes it from the line 117 insofar as it is placed upstream ofthe cold box 24, more precisely between the reforming unit 101 and thecarbon dioxide purification device 22. The line 29 is provided with aflow control valve 30 and with a flowmeter 31, both connected to themonitoring, calculation and control unit 121.

In steady-state operation, the valves 118 and 30 are closed and theinstallation is in conventional operation, which is known per se.

During a sudden and unscheduled shutdown of the purification unit 104,the valve 115 closes progressively, while the valve 118, controlled bythe unit 121, is opened by following a procedure similar to theprocedure, described above, which is employed when the purification unit4 of the installation shown in FIG. 1 is suddenly shut down. Oncompletion of this procedure, the portion of the installation whichextends from the reforming unit 101 to the cold box 24 has preserved asubstantially steady-state operating regime, which offers twoadvantages. Firstly, it avoids the slow and costly restart of thereforming unit 101. Secondly, the production of carbon monoxide can becontinued despite the shutdown of the purification unit 104.

If the unscheduled shutdown concerns the cold box 24, which results inthe consecutive shutdown of the purification unit 104, a proceduresimilar to the procedure explained above, which is employed during theshutdown of the purification unit 4 of the installation shown in FIG. 1,is followed. The valve 30, controlled by the unit 121, then plays asimilar role to that of the valve 18, and it is opened in order tocompensate for the progressive closure of the valve 115. Thus, thereforming unit 101 is kept in operation.

Furthermore, the two procedures, described above, which are designed tobe followed, one during start-up of the installation shown in FIG. 1,and the other during a reduction in the quantity of hydrogen produced bythis installation, can also advantageously be employed in theinstallation shown in FIG. 2, their transposition by a person skilled inthe art considered here posing no particular difficulty.

As a variant, one of the lines 29 and 117 can naturally be eliminated.

Moreover, the variants considered for the installation shown in FIG. 1may be adapted to the installation shown in FIG. 2.

Furthermore, the units 1 and 101 may be of various types. They may, forexample, be configured for the use either of simple steam methanereforming (SMR), or a convective type of steam methane reforming (TCR).

Moreover, other sorts of synthesis gas generators than the units 1 and101 for steam methane reforming can be used for the purpose of producingthe hydrogen-rich synthesis gas. For example, this could be a chemicalreactor, designed for the application of a catalytic or non-catalyticreaction.

In addition, the purification units 4 and 104 can be designed implementvarious sorts of processes. For example, they may be of the type basedon selective adsorption by cyclic pressure variation, or may be formedfrom a cryogenic separation cold box, or could even use the principle ofscrubbing with amines.

Similarly, the cold box 24 can be replaced with a separation unit ofanother type, designed to extract the carbon monoxide present in thesynthesis gas by a method other than the cryogenic method. For example,it can be replaced with a selective membrane device.

Moreover, particularly if the synthesis gas is produced by means of achemical reactor, the burners 6 can be used to equip not the reformingunit 1 or 101, replaced with this chemical reactor as required, butanother device such as a furnace or a steam production boiler, it beingpossible, for example, for this other device to form part of aproduction line other than the one in which the purification unit 4 or104 is arranged.

It will be understood that many additional changes in the details,materials, steps and arrangement of parts, which have been hereindescribed in order to explain the nature of the invention, may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims. Thus, the presentinvention is not intended to be limited to the specific embodiments inthe examples given above.

1. An installation for producing at least hydrogen, comprising: i) apurification unit configured to separate hydrogen from a synthesis gasand produce a waste gas separate from the hydrogen; ii) a first line forconveying the synthesis gas to the purification unit; iii) a second linefor conveying the waste gas from the purification unit to burners; iv) abuffer tank placed in said second line; and v) a third line, whereinsaid third line equipped with a first flow control valve and connectssaid first line to said second line, further comprising a second flowcontrol valve provided downstream of the buffer tank, wherein said thirdline is connected to said second line downstream of said second controlvalve.
 2. The installation of claim 1, further comprising at least afirst and a second flowmeter that are placed to measure the flow ratesin said first and said second control valves respectively, a unit forcontrolling said flow rates and for calculating and controlling thedegree of opening of each of said first and second control valves.
 3. Aninstallation for producing at least hydrogen, comprising: i) apurification unit configured to separate hydrogen from a synthesis gasand produce a waste gas separate from the hydrogen; ii) a first line forconveying the synthesis gas to the purification unit; iii) a second linefor conveying the waste gas from the purification unit to burners; iv) abuffer tank placed in said second line; and a third line, wherein saidthird line equipped with a first flow control valve and connects saidfirst line to said second line, further comprising a unit for reformingmethane with steam, which is provided with said burners for its heatingand which is intended for producing the hydrogen-rich synthesis gas,wherein said purification unit is located downstream of said reformingunit and intended for producing hydrogen extracted from the synthesisgas, further comprising a separation unit located between said reformingunit and said purification unit and intended to extract the carbonmonoxide present in the synthesis gas, wherein a fourth line which isequipped with another flow control valve and connects said first line tosaid second line, said third and fourth lines being connected to saidfirst line downstream and upstream of the separation unit respectively.4. The installation of claim 3, wherein said separation unit is acryogenic separation cold box.
 5. The installation of claim 3, furthercomprising a carbon dioxide purification device and a desiccation devicewhich are placed between said reforming unit and said separation unit,wherein said fourth line is connected to the first line upstream of saidcarbon dioxide purification device and of said desiccation device.
 6. Amethod comprising: i) extracting hydrogen from a synthesis gas in apurification unit, wherein a first line conveys the synthesis gas to thepurification unit; ii) recovering a waste gas from the purification unitvia a second line; iii) storing said waste gas in a buffer tank placedin the second line; iv) supplying, via the second line, one or moreburners with at least said waste gas, and further comprising, followingan unscheduled shutdown of the purification unit: i) continuing tosupply said burners, at least initially, with said gas from said buffertank; and ii) opening progressively a first flow control valve of athird line connecting the first line to the second line in order tosupply said burners with an increasing quantity of replacement gasconsisting of at least a portion of said synthesis gas.
 7. The method ofclaim 6, wherein said installation further comprises a second flowcontrol valve provided downstream of said buffer tank, wherein saidthird line is connected to said second line downstream of said secondcontrol valve, the method further comprising: i) closing progressivelysaid second flow control valve; ii) measuring continuously the flow rateof said waste gas being supplied to said burners; iii) calculatingcontinuously, in real time, the theoretical flow rate of replacement gasto be burned in order to compensate for the decrease in the flow rate ofsaid waste gas being supplied to said burners; and iv) regulating theactual flow rate of the replacement gas supplied to said burners toabout said calculated theoretical flow rate, by adjusting the degree ofopening of said first flow control valve.
 8. A method comprising:providing an installation for producing at least hydrogen, comprising:i) a purification unit configured to separate hydrogen from a synthesisgas and produce a waste gas; ii) a first line for conveying thesynthesis gas to the purification unit; iii) a second line for conveyingthe waste gas from the purification unit to burners; iv) a buffer tankplaced in said second line; v) a third line, wherein said third lineequipped with a flow control valve and connects said first line to saidsecond line; and vi) a unit for reforming methane with steam, which isprovided with said burners for its heating and which is intended forproducing the hydrogen-rich synthesis gas, wherein said purificationunit is located downstream of said reforming unit and intended forproducing hydrogen extracted from the synthesis gas, wherein starting upthe installation comprises: i) a first step, wherein said methanereforming unit is progressively started up by supplying said burnerswith at least a portion of the synthesis gas produced by said reformingunit, this portion of the synthesis gas being taken by means of saidthird line; and ii) a second step, wherein said purification unit, whichproduces a waste gas, is started up, and said burners are supplied withan increasing share of waste gas progressively replacing the portion ofsynthesis gas supplied to the burners.
 9. A method comprising: a)reacting in a reforming unit, a gas containing methane with steam, toproduce a hydrogen-rich synthesis gas; b) extracting in a purificationunit, the hydrogen present in the synthesis gas, wherein a first lineconveys the synthesis gas to the purification unit; c) recovering awaste gas from the purification unit via a second line; d) supplying oneor more burners with said waste gas via the second line; and e) heatingthe reforming unit by burning a supplemental auxiliary fuel, wherein, atleast initially: i) the flow rate of synthesis gas for treatment in thepurification unit is reduced by removing a portion thereof by means of athird line connecting the first line and the second line; ii) thisportion is used to supply the burners; and iii) the flow rate of thesupplementarily burned auxiliary fuel is simultaneously reduced.